The rise of social media use in young people has sparked concern about the impact of cyber-victimisation on mental health. Although cyber-victimisation is associated with mental health problems, it is not known whether such associations reflect genetic and environmental confounding.

We used the co-twin control design to test the direct association between cyber-victimisation and multiple domains of mental health in young people. Participants were 7708 twins drawn from the Twins Early Development Study, a UK-based population cohort followed from birth to age 22.

Monozygotic twins exposed to greater levels of cyber-victimisation had more symptoms of internalising, externalising and psychotic disorders than their less victimised co-twins at age 22, even after accounting for face-to-face peer victimisation and prior mental health. However, effect sizes from the most stringent monozygotic co-twin control analyses were decreased by two thirds from associations at the individual level [pooled β across all mental health problems = 0.06 (95% CI 0.03–0.10) v. 0.17 (95% CI 0.15–0.19) in individual-level analyses].

Cyber-victimisation has a small direct association with multiple mental health problems in young people. However, a large part of the association between cyber-victimisation and mental health is due to pre-existing genetic and environmental vulnerabilities and co-occurring face-to-face victimisation. Therefore, preventative interventions should target cyber-victimisation in conjunction with pre-existing mental health vulnerabilities and other forms of victimisation.